The objective of this proposal is to characterize the biologic attributes of the dendritic Thy-1 antigen-bearing cells which populate mouse epidermis (EC (Thy-1+)). Focusing first on their cellular attributes we plan to: 1a) refine methods for obtaining cell populations highly enriched for and highly depleted of them, 1b) attempt to propagate them in tissue culture with specialized growth media, 1c) obtain stable cell lines through cell fusion and viral transformation, 2) complete the phenotypic characterization of EC(Thy-1+) in adult epidermis and to compare these attributes with those of other related epidermal cells, 3) assess the ontogeny and migratory patterns of EC(Thy-1+) during the perinatal period after skin grafting, and under the influence of specific drugs (a phorbol ester and corticosteroids), and physical maneuvers (stratum corneum removal and UVB radiation), and 4) test a series of hypotheses concerning functional attributes of EC(Thy-1+), including a. They are T lymphocytes, b. They are non-T lymphocytes, c. They are antigen presenting cells. Functional properties will be tested in vitro and with in vivo studies in which EC(Thy-1+) are purified, treated, and reintroduced by various routes into naive recipients.